Amanitin Conjugates

ABSTRACT

The invention relates to a conjugate comprising (a) an amatoxin comprising (i) an amino acid 4 with a 6′-deoxy position; and (ii) an amino acid 8 with an S-deoxy position; (b) a target-binding moiety; and (c) optionally a linker linking said amatoxin and said target-binding moiety. The invention furthermore relates to a pharmaceutical composition comprising such conjugate.

FIELD OF THE INVENTION

The invention relates to a conjugate comprising (a) an amatoxincomprising (i) an amino acid 4 with a 6′-deoxy position; and (ii) anamino acid 8 with an S-deoxy position; (b) a target-binding moiety; and(c) optionally a linker linking said amatoxin and said target-bindingmoiety. The invention furthermore relates to a pharmaceuticalcomposition comprising such conjugate.

BACKGROUND OF THE INVENTION

Amatoxins are cyclic peptides composed of 8 amino acids that are foundin Amanita phalloides mushrooms (see FIG. 1). Amatoxins specificallyinhibit the DNA-dependent RNA polymerase II of mammalian cells, andthereby also the transcription and protein biosynthesis of the affectedcells. Inhibition of transcription in a cell causes stop of growth andproliferation. Though not covalently bound, the complex between amanitinand RNA-polymerase II is very tight (K_(D)=3 nM). Dissociation ofamanitin from the enzyme is a very slow process, thus making recovery ofan affected cell unlikely. When the inhibition of transcription laststoo long, the cell will undergo programmed cell death (apoptosis).

The use of amatoxins as cytotoxic moieties for tumour therapy hadalready been explored in 1981 by coupling an anti-Thy 1.2 antibody toα-amanitin using a linker attached to the indole ring of Trp (amino acid4; see FIG. 1) via diazotation (Davis & Preston, Science 213 (1981)1385-1388). Davis & Preston identified the site of attachment asposition 7′. Morris & Venton demonstrated as well that substitution atposition 7′ results in a derivative, which maintains cytotoxic activity(Morris & Venton, Int. J. Peptide Protein Res. 21 (1983) 419-430).

Patent application EP 1 859 811 A1 (published Nov. 28, 2007) describedconjugates, in which the γ C-atom of amatoxin amino acid 1 of β-amanitinwas directly coupled, i.e. without a linker structure, to albumin or tomonoclonal antibody HEA125, OKT3, or PA-1. Furthermore, the inhibitoryeffect of these conjugates on the proliferation of breast cancer cells(MCF-7), Burkitt's lymphoma cells (Raji) and T-lymphoma cells (Jurkat)was shown. The use of linkers was suggested, including linkerscomprising elements such as amide, ester, ether, thioether, disulfide,urea, thiourea, hydrocarbon moieties and the like, but no suchconstructs were actually shown, and no more details, such as attachmentsites on the amatoxins, were provided.

Patent applications WO 2010/115629 and WO 2010/115630 (both publishedOct. 14, 2010) describe conjugates, where antibodies, such as anti-EpCAMantibodies such as humanized antibody huHEA125, are coupled to amatoxinsvia (i) the γ C-atom of amatoxin amino acid 1, (ii) the 6′ C-atom ofamatoxin amino acid 4, or (iii) via the δ C-atom of amatoxin amino acid3, in each case either directly or via a linker between the antibody andthe amatoxins. The suggested linkers comprise elements such as amide,ester, ether, thioether, disulfide, urea, thiourea, hydrocarbon moietiesand the like. Furthermore, the inhibitory effects of these conjugates onthe proliferation of breast cancer cells (cell line MCF-7), pancreaticcarcinoma (cell line Capan-1), colon cancer (cell line Colo205), andcholangiocarcinoma (cell line OZ) were shown.

Patent application WO 2012/119787 describes that target-binding moietiescan be attached to amatoxins via linkers at additional attachment siteson tryptophan amino acid 4, namely positions 1′-N, without interferencewith the interaction of such amatoxins with their target, theDNA-dependent RNA polymerase II of mammalian cells.

It is known that amatoxins are relatively non-toxic when coupled tolarge biomolecule carriers, such as antibody molecules, and that theyexert their cytotoxic activity only after the biomolecule carrier iscleaved off. In light of the toxicity of amatoxins, particularly forliver cells, it is of outmost importance that amatoxin conjugates fortargeted tumour therapy remain highly stable after administration inplasma, and that the release of the amatoxin occurs afterinternalization in the target cells. In this context, minor improvementsof the conjugate stability may have drastic consequences for thetherapeutic window and the safety of the amatoxin conjugates fortherapeutic approaches.

Patent application WO 2012/041504 describes conjugates of an amatoxinwith a binding molecule, which use a urea moiety as linker to thebinding molecule. Such linkage could be shown to be significantly morestable than an ester linkage.

Thus, significant progress has already been made in the development ofamatoxin-based conjugates for therapeutic uses. However, the presentinventors have found that constructs based on α- and β-amatoxin were notfully stable under stress conditions in plasma and resulted in asubstantial degree of cross-linked products (see FIGS. 2 to 4). However,the stability of the conjugates comprising a highly toxic amatoxin is ofutmost importance for the envisaged use as a therapeutic molecule foradministration to human beings.

OBJECT OF THE INVENTION

Thus, there was still a great need for amatoxin variants with animproved stability. The solution to this problem, i.e. theidentification of certain modifications to the backbone of eight aminoacid residues forming the basic amatoxin structure was neither providednor suggested by the prior art.

SUMMARY OF THE INVENTION

The present invention is based on the unexpected observation that avariant form of amatoxins with (i) an amino acid 4 with a 6′-deoxyposition; and (ii) an amino acid 8 with an S-deoxy position, shows anincreased stability under stress conditions and an improved therapeuticindex.

Thus, in one aspect the present invention relates to a conjugatecomprising (a) an amatoxin comprising (i) an amino acid 4 with a6′-deoxy position; and (ii) an amino acid 8 with an S-deoxy position;(b) a target-binding moiety; and (c) optionally a linker linking saidamatoxin and said target-binding moiety. In particular, the optionallinker of (c) is present and is a cleavable linker.

In a second aspect, the present invention relates to a pharmaceuticalcomposition comprising the conjugate of the present invention.

In a third aspect, the present invention relates to a conjugate of thepresent invention for use in the treatment of cancer in a patient,particularly wherein the cancer is selected from the group consisting ofbreast cancer, pancreatic cancer, cholangiocarcinoma, colorectal cancer,lung cancer, prostate cancer, ovarian cancer, prostate cancer, stomachcancer, kidney cancer, malignant melanoma, leukemia, and malignantlymphoma.

In a fourth aspect, the present invention relates to a constructcomprising (a) an amatoxin comprising (i) an amino acid 4 with a6′-deoxy position; and (ii) an amino acid 8 with an S-deoxy position;and (c) a linker moiety, particularly a linker that is cleavable,carrying a reactive group for linking said amatoxin to a target-bindingmoiety.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the structural formulae of different amatoxins. The numbersin bold type (1 to 8) designate the standard numbering of the eightamino acids forming the amatoxin. The standard designations of the atomsin amino acids 1, 3 and 4 are also shown (Greek letters α to γ, Greekletters α to δ, and numbers from 1′ to 7′, respectively).

FIG. 2 shows the results of a stress testing experiment in ananti-amanitin Western blot. A trastuzumab-amanitin conjugate(Her-30.0643; lysine conjugation via 6′-OH; stable linker) was incubatedfor 5 days at 37° C. in PBS, pH 7.4, which led to extensive inter- andintrachain cross-linking; cross-linking of antibody chains could beprevented by addition of free cysteine.

FIG. 3 shows that α-Amanitin shows a strong reactivity with cysteine inPBS buffer, pH 7.4. 1 mg/mL α-amanitin 10 mg/mL cysteine in PBS, pH 7.4at 37° C. after 24 h, 48 h and 6 d RP-HPLC C18.

FIG. 4 shows that β-Amanitin shows a strong reactivity with cysteine inPBS buffer, pH 7.4. 1 mg/mL β-amanitin 10 mg/mL cysteine in PBS, pH 7.4at 37° C. after 24 h, 48 h and 6 d RP-HPLC C18.

FIG. 5 shows that a 6″-deoxy variant at amino acid 4 (“amanin”) shows areduced reactivity with cysteine. 1 mg/mL amanin 10 mg/mL cysteine inPBS, pH 7.4 at 37° C. after 24 h, 48 h and 6 d RP-HPLC C18.

FIG. 6 and FIG. 7 show that a double deoxy variant HDP 30.2105 (6′-deoxyat amino acid 4 and S-deoxy at amino acid 8; formula I with R³═—OR⁵ andeach R⁵═H) shows complete absence of reactivity with cysteine. 1 mg/mLHDP 30.2105, 10 mg/mL cysteine in PBS, pH 7.4 at 37° C. after 24 h, 48 hand 6 d RP-HPLC C18; * impurity.

FIG. 8 shows alpha-amanitin derivative HDP 30.1699 with cleavable linkerat AA4-6-OH moiety, beta-amanitin derivative HDP 30.2060 with cleavablelinker at AA1 γ-position and double deoxy amatoxin variant HDP 30.2115with cleavable linker at AA1 α-position.

FIG. 9 shows Western-Blot analysis of amatoxin derivatives HDP 30.1699,HDP 30.2060 and HDP 30.2115 conjugated to T-D265C antibody afterincubation at 37° C. in human plasma, mouse plasma an phosphate bufferedsaline (PBS) for 0, 4 and 10 days. Detection was done with a polyclonalanti-amanitin antibody from rabbit and an anti-rabbit antibodyconjugated to horseradish peroxidase. HDP 30.1699 and HDP 30.2060 showedconsiderable cross-links and loss of the amatoxin moiety. Double deoxyamanitin variant HDP 30.2115 shows high stability and significantlyreduced cross-links.

FIG. 10 shows cytotoxicity of amatoxin derivatives HDP 30.1699, HDP30.2060 and HDP 30.2115 conjugated to T-D265C antibody. Test items wereincubated in human plasma at 37° C. for 0 an 4 days. Cytotoxicity assaywere performed on SKBR-3 cells for 96 h. HDP 30.1699 and HDP 30.2060based ADCs show remarkable loss of cytotoxicity after 4 days plasmastressing whereas deoxygenated derivative HDP 30.2115 shows stillpicomolar activity

FIG. 11 shows cytotoxicity of amatoxin derivatives HDP 30.1699, HDP30.2060 and HDP 30.2115 conjugated to T-D265C antibody. Test items wereincubated in mouse plasma at 37° C. for 0 an 4 days. Cytotoxicity assaywere performed on SKBR-3 cells for 96 h. HDP 30.1699 and HDP 30.2060based ADCs show remarkable loss of cytotoxicity after plasma stressingwhereas deoxygenated derivative HDP 30.2115 remains almost unchanged.

FIG. 12 shows cytotoxicity of amatoxin derivatives HDP 30.1699, HDP30.2060 and HDP 30.2115 conjugated to T-D265C antibody. Test items wereincubated in PBS at 37° C. for 0 an 4 days. Cytotoxicity assay wereperformed on SKBR-3 cells for 96 h. All ADCs show adequate stability tonon-enzymatic environment.

FIG. 13 compares the antitumoral activity of different chiBCE19-D265Cantibody-amatoxin conjugates in Raji s.c. xenograft model—single doseexperiment. Depending on linker and toxin structure significantdifferences in antitumoral activity have been observed. The deoxy-amaninvariant chiBCE19-30.2115 (6′-deoxy at amino acid 4 and S-deoxy at aminoacid 8) showed best antitumoral activity of all amatoxin ADCs, with asignificantly better therapeutic index than corresponding cleavablelinker ADC chiBCE19-30.1699 (lysine conjugation via 6′-OH; S═O at aminoacid 8).

FIG. 14 shows the Kaplan Meier survival analysis in a systemic Rajitumor model—single dose experiment. In brief, 2.5×10⁶ Raji (humanBurkitt's lymphoma) tumour cells in 200 μL PBS/mouse were inoculatedintravenously on day 0. Therapy (single dose, iv) was initiated on day 3post tumor cell inoculation. The deoxy-amanin variant chiBCE19-30.2115(6′-deoxy at amino acid 4 and S-deoxy at amino acid 8) showed superiorsurvival over α-amanitin derivatives HDP 30.1699, HDP 30.0880 and HDP30.0643 as well as the corresponding MMAE-derivative.

DETAILED DESCRIPTION OF THE INVENTION

Before the present invention is described in detail below, it is to beunderstood that this invention is not limited to the particularmethodology, protocols and reagents described herein as these may vary.It is also to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto limit the scope of the present invention which will be limited onlyby the appended claims. Unless defined otherwise, all technical andscientific terms used herein have the same meanings as commonlyunderstood by one of ordinary skill in the art.

Particularly, the terms used herein are defined as described in “Amultilingual glossary of biotechnological terms: (IUPACRecommendations)”, Leuenberger, H. G. W, Nagel, B. and Kölbl, H. eds.(1995), Helvetica Chimica Acta, CH-4010 Basel, Switzerland).

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the word “comprise”, and variations such as“comprises” and “comprising”, will be understood to imply the inclusionof a stated integer, composition or step or group of integers or steps,while any additional integer, composition or step or group of integers,compositions or steps may optionally be present as well, includingembodiments, where no additional integer, composition or step or groupof integers, compositions or steps are present. In such latterembodiments, the term “comprising” is used coterminous with “consistingof”.

Several documents are cited throughout the text of this specification.Each of the documents cited herein (including all patents, patentapplications, scientific publications, manufacturer's specifications,instructions, GenBank Accession Number sequence submissions etc.),whether supra or infra, is hereby incorporated by reference in itsentirety to the extent possible under the respective patent law. Nothingherein is to be construed as an admission that the invention is notentitled to antedate such disclosure by virtue of prior invention.

The present invention will now be further described. In the followingpassages different aspects of the invention are defined in more detail.Each aspect so defined may be combined with any other aspect or aspectsunless clearly indicated to the contrary. In particular, any featureindicated as being preferred or advantageous may be combined with anyother feature or features indicated as being preferred or advantageous.

The present invention is based on the unexpected observation that avariant form of amatoxins with (i) an amino acid 4 with a 6′-deoxyposition; and (ii) an amino acid 8 with an S-deoxy position, shows anincreased stability under stress conditions and an improved therapeuticindex.

Thus, in one aspect the present invention relates to a conjugatecomprising (a) an amatoxin comprising (i) an amino acid 4 with a6′-deoxy position; and (ii) an amino acid 8 with an S-deoxy position;(b) a target-binding moiety; and (c) optionally a linker linking saidamatoxin and said target-binding moiety. In particular, the optionallinker of (c) is present and is a cleavable linker.

Zhao et al., ChemBioChem 16 (2015) 1420-1425, reported the synthesis ofsuch a di-deoxy amatoxin core. However, the method of Zhao et al.resulted in a mixture of four different diastereomers, with only one ofthem exhibiting the desired toxicity of the natural products. Thus, asfully correctly identified by Zhao et al., the production of the singletoxic diastereomer in pure form still represented a key need (Zhao etal. loc. cit., p. 1424, left column). While Zhao et al. proposed alengthy list of potential routes to achieve such result, the proposalsgiven are not more than an invitation to perform research. Additionally,while Zhao et al. could confirm that the synthetic variant essentiallymaintains the toxicity of the corresponding natural product, the do notshow any advantages of their new compound, and in particular do notprovide any teaching or even any suggestion that amatoxin derivativeswith a di-deoxy core in accordance with the present invention show anincreased stability under stress conditions in plasma and do not resultin cross-linked products. Thus, Zhao et al. do not provide anyparticular incentive for one of ordinary skill in the art to undertakethe required efforts for such research activities.

In a particular embodiment, the present invention relates to a conjugatehaving structure I

wherein:

-   -   R² is S;    -   R³ is selected from —NHR⁵, —NH—OR⁵, and —OR⁵;    -   R⁴ is H; and    -   wherein one of R⁵ is -L_(n)-X, wherein L is a linker,        particularly a cleavable linker, n is selected from 0 and 1, and        X is a target-binding moiety, and wherein the remaining R⁵ are        H.

In the context of the present invention, the term “amatoxin” includesall cyclic peptides composed of 8 amino acids as isolated from the genusAmanita and described in Wieland, T. and Faulstich H. (Wieland T,Faulstich H., CRC Crit Rev Biochem. 5 (1978) 185-260), which comprisethe specific positions according to (i) (i.e. where the indole moiety ofthe amino acid residue tryptophan has no oxygen-containing substituentat position 6′, particularly where position 6′ carries a hydrogen atom)and (ii) (i.e. in which the thioether sulfoxide moiety of naturallyoccurring amatoxins is replaced by a sulfide), and furthermore includesall chemical derivatives thereof; further all semisynthetic analoguesthereof; further all synthetic analogues thereof built from buildingblocks according to the master structure of the natural compounds(cyclic, 8 amino acids), further all synthetic or semisyntheticanalogues containing non-hydroxylated amino acids instead of thehydroxylated amino acids, further all synthetic or semisyntheticanalogues, in each case wherein any such derivative or analogue carriesat least the positions (i) and (ii) mentioned above and is functionallyactive by inhibiting mammalian RNA polymerase II.

Functionally, amatoxins are defined as peptides or depsipeptides thatinhibit mammalian RNA polymerase II. Preferred amatoxins are those witha functional group (e.g. a carboxylic group or carboxylic acidderivative such as a carboxamide or hydroxamic acid, an amino group, ahydroxy group, a thiol or a thiol-capturing group) that can be reactedwith linker molecules or target-binding moieties as defined above.Amatoxins which are particularly suitable for the conjugates of thepresent invention are di-deoxy variants of α-amanitin, β-amanitin,γ-amanitin, ε-amanitin, amanullin, or amanullinic acid, or mono-deoxyvariants of amanin, amaninamide, γ-amanin, or γ-amaninamide as shown inFIG. 1 as well as salts, chemical derivatives, semisynthetic analogues,and synthetic analogues thereof.

In a particular embodiment, the conjugate of the present invention has apurity greater than 90%, particularly greater than 95%.

In the context of the present invention, the term “purity” refers to thetotal amount of conjugates being present. A purity of greater than 90%,for example, means that in 1 mg of a composition comprising a conjugateof the present invention, there are more than 90%, i.e. more than 900μg, of such conjugate. The remaining part, i.e. the impurities mayinclude unreacted starting material and other reactants, solvents,cleavage products and/or side products.

In a particular embodiment, a composition comprising a conjugate of thepresent invention comprises more than 100 mg, in particular more than500 mg, and more particularly more than 1 g of such conjugate. Thus,trace amount of a conjugate of the present invention that arguably maybe present in complex preparations of conjugates of the prior art, e.g.from partial reduction of naturally occurring sulfoxides, are explicitlyexcluded.

The term “target-binding moiety”, as used herein, refers to any moleculeor part of a molecule that can specifically bind to a target molecule ortarget epitope. Preferred target-binding moieties in the context of thepresent application are (i) antibodies or antigen-binding fragmentsthereof; (ii) antibody-like proteins; and (iii) nucleic acid aptamers.“Target-binding moieties” suitable for use in the present inventiontypically have a molecular mass of 40 000 Da (40 kDa) or more.

As used herein, a first compound (e.g. an antibody) is considered to“specifically bind” to a second compound (e.g. an antigen, such as atarget protein), if it has a dissociation constant K_(D) to said secondcompound of 100 μM or less, particularly 50 μM or less, particularly 30μM or less, particularly 20 μM or less, particularly 10 μM or less,particularly 5 μM or less, more particularly 1 μM or less, moreparticularly 900 nM or less, more particularly 800 nM or less, moreparticularly 700 nM or less, more particularly 600 nM or less, moreparticularly 500 nM or less, more particularly 400 nM or less, moreparticularly 300 nM or less, more particularly 200 nM or less, even moreparticularly 100 nM or less, even more particularly 90 nM or less, evenmore particularly 80 nM or less, even more particularly 70 nM or less,even more particularly 60 nM or less, even more particularly 50 nM orless, even more particularly 40 nM or less, even more particularly 30 nMor less, even more particularly 20 nM or less, and even moreparticularly 10 nM or less.

In the context of the present application the terms “target molecule”and “target epitope”, respectively, refers to an antigen and an epitopeof an antigen, respectively, that is specifically bound by atarget-binding moiety. Particularly the target molecule is atumour-associated antigen, in particular an antigen or an epitope whichis present on the surface of one or more tumour cell types in anincreased concentration and/or in a different steric configuration ascompared to the surface of non-tumour cells. Particularly, said antigenor epitope is present on the surface of one or more tumour cell types,but not on the surface of non-tumour cells. In particular embodiments,the target-binding moiety specifically binds to an epitope of an antigenselected from: PSMA, CD19, CD269, sialyl Lewis^(a), HER-2/neu andepithelial cell adhesion molecule (EpCAM). In other embodiments, saidantigen or epitope is preferentially expressed on cells involved inautoimmune diseases. In particular such embodiments, the target-bindingmoiety specifically binds to an epitope of the IL-6 receptor (IL-6R).

The term “antibody or antigen binding fragment thereof”, as used herein,refers to immunoglobulin molecules and immunologically active portionsof immunoglobulin molecules, i.e. molecules that contain anantigen-binding site that immunospecifically binds an antigen. Thus, theterm “antigen-binding fragments thereof” refers to a fragment of anantibody comprising at least a functional antigen-binding domain. Alsocomprised are immunoglobulin-like proteins that are selected throughtechniques including, for example, phage display to specifically bind toa target molecule, e.g. to a target protein selected from: PSMA, CD19,CD269, sialyl Lewis^(a), Her-2/neu and EpCAM. The immunoglobulinmolecules of the invention can be of any type (e.g., IgG, IgE, IgM, IgD,IgA and IgY), class (e.g., IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2) orsubclass of immunoglobulin molecule. “Antibodies and antigen-bindingfragments thereof” suitable for use in the present invention include,but are not limited to, polyclonal, monoclonal, monovalent, bispecific,heteroconjugate, multispecific, human, humanized (in particularCDR-grafted), deimmunized, or chimeric antibodies, single chainantibodies (e.g. scFv), Fab fragments, F(ab′)₂ fragments, fragmentsproduced by a Fab expression library, diabodies or tetrabodies (HolligerP. et al., Proc Natl Acad Sci USA. 90 (1993) 6444-8), nanobodies,anti-idiotypic (anti-Id) antibodies (including, e.g., anti-Id antibodiesto antibodies of the invention), and epitope-binding fragments of any ofthe above.

In some embodiments the antigen-binding fragments are humanantigen-binding antibody fragments of the present invention and include,but are not limited to, Fab, Fab′ and F(ab′)₂, Fd, single-chain Fvs(scFv), single-chain antibodies, disulfide-linked Fvs (dsFv) andfragments comprising either a VL or VH domain. Antigen-binding antibodyfragments, including single-chain antibodies, may comprise the variabledomain(s) alone or in combination with the entirety or a portion of thefollowing: hinge region, CL, CH1, CH2, and CH3 domains. Also included inthe invention are antigen-binding fragments also comprising anycombination of variable domain(s) with a hinge region, CL, CH1, CH2, andCH3 domains.

Antibodies usable in the invention may be from any animal originincluding birds and mammals. Particularly, the antibodies are fromhuman, rodent (e.g. mouse, rat, guinea pig, or rabbit), chicken, pig,sheep, goat, camel, cow, horse, donkey, cat, or dog origin. It isparticularly preferred that the antibodies are of human or murineorigin. As used herein, “human antibodies” include antibodies having theamino acid sequence of a human immunoglobulin and include antibodiesisolated from human immunoglobulin libraries or from animals transgenicfor one or more human immunoglobulin and that do not express endogenousimmunoglobulins, as described for example in U.S. Pat. No. 5,939,598 byKucherlapati & Jakobovits.

The term “antibody-like protein” refers to a protein that has beenengineered (e.g. by mutagenesis of loops) to specifically bind to atarget molecule. Typically, such an antibody-like protein comprises atleast one variable peptide loop attached at both ends to a proteinscaffold. This double structural constraint greatly increases thebinding affinity of the antibody-like protein to levels comparable tothat of an antibody. The length of the variable peptide loop typicallyconsists of 10 to 20 amino acids. The scaffold protein may be anyprotein having good solubility properties. Particularly, the scaffoldprotein is a small globular protein. Antibody-like proteins includewithout limitation affibodies, anticalins, and designed ankyrin repeatproteins (for review see: Binz et al., Nat Biotechnol. 2005, 1257-68).Antibody-like proteins can be derived from large libraries of mutants,e.g. be panned from large phage display libraries and can be isolated inanalogy to regular antibodies. Also, antibody-like binding proteins canbe obtained by combinatorial mutagenesis of surface-exposed residues inglobular proteins.

The term “nucleic acid aptamer” refers to a nucleic acid molecule thathas been engineered through repeated rounds of in vitro selection orSELEX (systematic evolution of ligands by exponential enrichment) tobind to a target molecule (for a review see: Brody and Gold, JBiotechnol. 74 (2000) 5-13). The nucleic acid aptamer may be a DNA orRNA molecule. The aptamers may contain modifications, e.g. modifiednucleotides such as 2′-fluorine-substituted pyrimidines.

A “linker” in the context of the present invention refers to a structurethat is connecting two components, each being attached to one end of thelinker. In the case of the linker being a bond, a direct linkage ofamatoxin to the antibody may decrease the ability of the amatoxin tointeract with RNA polymerase II. In particular embodiments, the linkerincreases the distance between two components and alleviates stericinterference between these components, such as in the present casebetween the antibody and the amatoxin. In particular embodiments, thelinker has a continuous chain of between 1 and 30 atoms (e.g. 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,23, 24, 25, 26, 27, 28, 29, or 30 atoms) in its backbone, i.e. thelength of the linker is defined as the shortest connection as measuredby the number of atoms or bonds between the amatoxin moiety and theantibody, wherein one side of the linker backbone has been reacted withthe amatoxin and, the other side is available for reaction, or has beenreacted, with an antibody. In the context of the present invention, alinker particularly is a C₁₋₂₀-alkylene, C₁₋₂₀-heteroalkylene,C₂₋₂₀-alkenylene, C₂₋₂₀-heteroalkenylene, C₂₋₂₀-alkynylene,C₂₋₂₀-heteroalkynylene, cycloalkylene, heterocycloalkylene, arylene,heteroarylene, aralkylene, or a heteroaralkylene group, optionallysubstituted. The linker may contain one or more structural elements suchas carboxamide, ester, ether, thioether, disulfide, urea, thiourea,hydrocarbon moieties and the like. The linker may also containcombinations of two or more of these structural elements. Each one ofthese structural elements may be present in the linker more than once,e.g. twice, three times, four times, five times, or six times. In someembodiments the linker may comprise a disulfide bond. It is understoodthat the linker has to be attached either in a single step or in two ormore subsequent steps to the amatoxin and the antibody. To that end thelinker to be will carry two groups, particularly at a proximal anddistal end, which can (i) form a covalent bond to a group present in oneof the components to be linked, particularly an activated group on anamatoxin or the target binding-peptide or (ii) which is or can beactivated to form a covalent bond with a group on an amatoxin.Accordingly, it is preferred that chemical groups are at the distal andproximal end of the linker, which are the result of such a couplingreaction, e.g. an ester, an ether, a urethane, a peptide bond etc.

In particular embodiments, the linker L is a linear chain of between 1and 20 atoms independently selected from C, O, N and S, particularlybetween 2 and 18 atoms, more particularly between 5 and 16 atoms, andeven more particularly between 6 and 15 atoms. In particularembodiments, at least 60% of the atoms in the linear chain are C atoms.In particular embodiments, the atoms in the linear chain are linked bysingle bonds.

In particular embodiments. the linker L is an alkylene, heteroalkylene,alkenylene, heteroalkenylene, alkynylene, heteroalkynylene,cycloalkylene, heterocycloalkylene, arylene, heteroarylene, aralkylene,or a heteroaralkylene group, comprising from 1 to 4 heteroatoms selectedfrom N, O, and S, wherein said linker is optionally substituted.

The term “alkylene” refers to a bivalent straight chain saturatedhydrocarbon groups having from 1 to 20 carbon atoms, including groupshaving from 1 to 10 carbon atoms. In certain embodiments, alkylenegroups may be lower alkylene groups. The term “lower alkylene” refers toalkylene groups having from 1 to 6 carbon atoms, and in certainembodiments from 1 to 5 or 1 to 4 carbon atoms. Examples of alkylenegroups include, but are not limited to, methylene (—CH₂—), ethylene(—CH₂—CH₂—), n-propylene, n-butylene, n-pentylene, and n-hexylene.

The term “alkenylene” refers to bivalent straight chain groups having 2to 20 carbon atoms, wherein at least one of the carbon-carbon bonds is adouble bond, while other bonds may be single bonds or further doublebonds. The term “alkynylene” herein refers to groups having 2 to 20carbon atoms, wherein at least one of the carbon-carbon bonds is atriple bond, while other bonds may be single, double or further triplebonds. Examples of alkenylene groups include ethenylene (—CH═CH—),1-propenylene, 2-propenylene, 1-butenylene, 2-butenylene, 3-butenylene,and the like. Examples of alkynylene groups include ethynylene,1-propynylene, 2-propynylene, and so forth.

As used herein, “cycloalkylene” is intended to refer to a bivalent ringbeing part of any stable monocyclic or polycyclic system, where suchring has between 3 and 12 carbon atoms, but no heteroatom, and wheresuch ring is fully saturated, and the term “cycloalkenylene” is intendedto refer to a bivalent ring being part of any stable monocyclic orpolycyclic system, where such ring has between 3 and 12 carbon atoms,but no heteroatom, and where such ring is at least partially unsaturated(but excluding any arylene ring). Examples of cycloalkylenes include,but are not limited to, cyclopropylene, cyclobutylene, cyclopentylene,cyclohexylene, and cycloheptylene. Examples of cycloalkenylenes include,but are not limited to, cyclopentenylene and cyclohexenylene.

As used herein, the terms “heterocycloalkylene” and“heterocycloalkenylene” are intended to refer to a bivalent ring beingpart of any stable monocyclic or polycyclic ring system, where such ringhas between 3 and about 12 atoms, and where such ring consists of carbonatoms and at least one heteroatom, particularly at least one heteroatomindependently selected from the group consisting of N, O and S, withheterocycloalkylene referring to such a ring that is fully saturated,and heterocycloalkenylene referring to a ring that is at least partiallyunsaturated (but excluding any arylene or heteroarylene ring).

The term “arylene” is intended to mean a bivalent ring or ring systembeing part of any stable monocyclic or polycyclic system, where suchring or ring system has between 3 and 20 carbon atoms, but has noheteroatom, which ring or ring system consists of an aromatic moiety asdefined by the “4n+2” π electron rule, including phenylene.

As used herein, the term “heteroarylene” refers to a bivalent ring orring system being part of any stable mono- or polycyclic system, wheresuch ring or ring system has between 3 and 20 atoms, which ring or ringsystem consists of an aromatic moiety as defined by the “4n+2” πelectron rule and contains carbon atoms and one or more nitrogen,sulfur, and/or oxygen heteroatoms.

In the context of the present invention, the term “substituted” isintended to indicate that one or more hydrogens present in the backboneof a linker is replaced with a selection from the indicated group(s),provided that the indicated atom's normal valency, or that of theappropriate atom of the group that is substituted, is not exceeded, andthat the substitution results in a stable compound. The term “optionallysubstituted” is intended to mean that the linker is either unsubstitutedor substituted, as defined herein, with one or more substituents, asdefined herein. When a substituent is a keto (or oxo, i.e. ═O) group, athio or imino group or the like, then two hydrogens on the linkerbackbone atom are replaced. Exemplary substituents include, for example,alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl,aralkyl, heteroaralkyl, acyl, aroyl, heteroaroyl, carboxyl, alkoxy,aryloxy, acyloxy, aroyloxy, heteroaroyloxy, alkoxycarbonyl, halogen,(thio)ester, cyano, phosphoryl, amino, imino, (thio)amido, sulfhydryl,alkylthio, acylthio, sulfonyl, a sulfate, a sulfonate, a sulfamoyl, asulfonamido, nitro, azido, haloalkyl, including perfluoroalkyl (such astrifluoromethyl), haloalkoxy, alkylsulfanyl, alkylsulfinyl,alkylsulfonyl, alkylsulfonylamino, arylsulfonoamino, phosphoryl,phosphate, phosphonate, phosphinate, alkylcarboxy, alkylcarboxyamide,oxo, hydroxy, mercapto, amino (optionally mono- or di-substituted, e.g.by alkyl, aryl, or heteroaryl), imino, carboxamide, carbamoyl(optionally mono- or di-substituted, e.g. by alkyl, aryl, orheteroaryl), amidino, aminosulfonyl, acylamino, aroylamino,(thio)ureido, (arylthio)ureido, alkyl(thio)ureido,cycloalkyl(thio)ureido, aryloxy, aralkoxy, or —O(CH₂)_(n)—OH,—O(CH₂)_(n)—NH₂, —O(CH₂)_(n)COOH, —(CH₂)_(n)COOH, —C(O)O(CH₂)_(n)R,—(CH₂)_(n)N(H)C(O)OR, or —N(R)S(O)₂R wherein n is 1-4 and R isindependently selected from hydrogen, -alkyl, -alkenyl, -alkynyl,-cycloalkyl, -cycloalkenyl, —(C-linked-heterocycloalkyl),—(C-linked-heterocycloalkenyl), -aryl, and -heteroaryl, with multipledegrees of substitution being allowed. It will be understood by thoseskilled in the art that substituents, such as heterocycloalkyl, aryl,heteroaryl, alkyl, etc., or functional groups such as —OH, —NHR etc.,can themselves be substituted, if appropriate. It will also beunderstood by those skilled in the art that the substituted moietiesthemselves can be substituted as well when appropriate.

In particular embodiments, the linker L comprises a moiety selected fromone of the following moieties: a disulfide (—S—S—), an ether (—O—), athioether (—S—), an amine (—NH—), an ester (—O—C(═O)— or —C(═O)—O—), acarboxamide (—NH—C(═O)— or —C(═O)—NH—), a urethane (—NH—C(═O)—O— or—O—C(═O)—NH—), and a urea moiety (—NH—C(═O)—NH—).

In particular embodiments of the present invention, the linker Lcomprises a number of m groups selected from the list of: alkylene,alkenylene, alkynylene, cycloalkylene, heteroalkylene, heteroalkenylene,heteroalkynylene, heterocycloalkylene, arylene, heteroarylene,aralkylene, and a heteroaralkylene group, wherein each group mayoptionally be independently substituted, the linker further comprises anumber of n moieties independently selected from one of the followingmoieties: a disulfide (—S—S—), an ether (—O—), a thioether (—S—), anamine (—NH—), an ester (—O—C(═O)— or —C(═O)—O—), a carboxamide(—NH—C(═O)— or —C(═O)—NH—), a urethane (—NH—C(═O)—O— or —O—C(═O)—NH—),and a urea moiety (—NH—C(═O)—NH—), wherein m=n+1. In particularembodiments, m is 2 and n is 1, or m is 3 and n is 2. In particularembodiments, the linker comprises 2 or 3 unsubstituted alkylene groups,and 1 or 2, respectively, disulfide, ether, thioether, amine, ester,carboxamide, urethane or urea moieties linking the unsubstitutedalkylene groups.

In a particular embodiment, the linker L does not comprise aheteroarylene group.

In particular embodiments, the C atoms in the linear chain areindependently part of optionally substituted methylene groups (—CH₂—).In particular such embodiments, the optional substituents areindependently selected from halogen and C₁₋₆-alkyl, particularly methyl.

In particular embodiments, the linker L is a stable linker.

In the context of the present invention, the term “stable linker” refersto a linker that is stable (i) in the presence of enzymes, and (ii) inan intracellular reducing environment.

In particular embodiments, the stable linker does not contain (i) anenzyme-cleavable substructure, and/or (ii) a disulfide group. Inparticular such embodiments, the linker has a length of up to 12 atoms,particularly from 2 to 10, more particularly from 4 to 9, and mostparticularly from 6 to 8 atoms.

In particular other embodiments, the linker is a cleavable linker.

In the context of the present invention, the term “cleavable linker”refers to a linker that is (i) cleavable by an enzyme, or (ii) areducible linker. In particular embodiments, the term only refers to alinker that is cleavable by an enzyme (not to a reducible linker).

In the context of the present invention, the term “linker that iscleavable . . . by an enzyme” refers to a linker that can be cleaved byan enzyme, particularly by a lysosomal peptidase, such as Cathepsin B,resulting in the intracellular release of the toxin cargo conjugated tothe targeting antibody after internalization (see Dubowchik et al.,Bioconjug Chem. 13 (2002) 855-69). In particular embodiments, thecleavable linker comprises a dipeptide selected from: Phe-Lys, Val-Lys,Phe-Ala, Val-Ala, Phe-Cit and Val-Cit, particularly wherein thecleavable linker further comprises a p-aminobenzyl (PAB) spacer betweenthe dipeptides and the amatoxin.

In particular such embodiments, the cleavable linker comprises astructure L¹-L*-L²

-   -   wherein L¹ is a part of the linker that connects L* to the        amatoxin, in particular, wherein L¹ is connected to L* via a        —NH— or a —O— group, particularly a —C(═O)—NH—, a —C(═O)—NH—O—        or a —C(═O)—O— group, and    -   wherein L² is a part of the linker that connects L* to the        target-binding moiety, in particularly wherein L¹ is connected        to L* via a —(CH₂)_(m)— moiety, with m being an integer selected        from 1 to 8, in particular from 1 to 5, or via a —(CH₂CH₂O)_(n)—        moiety, with n being an integer selected from 1 to 3, in        particular from 1 to 2.

In particular other such embodiments, L* has the following structure

In particular embodiments, the linker L¹ is a linear chain of between 1and 4 atoms independently selected from C, O, N and S, particularlybetween 1 and 3 atoms, more particularly between 1 and 2 atoms, and evenmore just 1 atom. In particular embodiments, at least 50% of the atomsin the linear chain are C atoms. In particular embodiments, the atoms inthe linear chain are linked by single bonds.

In the context of the present invention, the term “reducible linker”refers to a linker that can be cleaved in the intracellular reducingenvironment, particularly a linker that contains a disulfide groups,resulting in the intracellular release of the toxin cargo conjugated tothe target-binding moiety after internalization by the intracellularreducing environment (see Shen et al., J. Biol. Chem. 260 (1985)10905-10908). In particular embodiments, the reducible linker comprisesa moiety

wherein R1 to R4 are independently selected from H and methyl.

In particular such embodiments, such cleavable linker has a length of upto 20 atoms, particularly from 6 to 18, more particularly from 8 to 16,and most particularly from 10 to 15 atoms. In particular suchembodiments, the part of the linker linking the amatoxin according tothe present invention and the cleavable disulfide group is a linearchain of 3 or 4 C atoms, particularly 3 C atoms. In particularembodiments, the 3 or 4 C atoms in the linear chain are linked by singlebonds. In particular embodiments, the linker is an n-propylene group.

In particular embodiments, said linker is present and is connected onone side to a position in the amatoxin of formula I selected from

-   -   (i) in the case of a conjugate of formula I with R³═—NHR⁵, the        nitrogen atom of the amide group at the γ C-atom of amatoxin        amino acid 1 (amide linkage);    -   (ii) in the case of a conjugate of formula I with R³═—OR⁵, the        oxygen atom of the acid group at the γ C-atom of amatoxin amino        acid 1 (ester linkage);    -   (iii) in the case of a conjugate of formula I with R³═—NHOR⁵,        the oxygen atom of the hydroxamic acid group at the γ C-atom of        amatoxin amino acid 1;    -   (iv) the oxygen atom of the hydroxy group at the δ C-atom of        amatoxin amino acid 3, particularly via an ester linkage, an        ether linkage or a urethane linkage; or    -   (v) the ring nitrogen of amino acid 4.

In particular such embodiments, said linker is present and is connectedon one side to a position in the amatoxin of formula I selected from(ii) to (v) shown above. In particular embodiments, said linker ispresent and is connected on one side to a position in the amatoxin offormula I selected from (iv) to (v) shown above.

Coupling of the linker to the target-binding moiety can be achieved by avariety of methods well known to one of ordinary skill in the art,particularly in the art of antibody-drug conjugates (ADCs).

In particular embodiments, said linker is connected to thetarget-binding moiety via a urea moiety ( . . . -linker-NH—C(═O)—NH—target-binding moiety). In particular such embodiments, the urea moietyresults from a reaction of a primary amine originally present in thetarget-binding moiety, such as an amino group of a lysine side chain,with a carbamic acid derivative . . . -linker-NH—C(O)—Z, wherein Z is aleaving group that can be replaced by a primary amine.

In particular other embodiments, said linker is present and is connectedto the target-binding moiety via a thioether moiety ( . . .-linker-S-target-binding moiety). Thus, in such embodiments, the presentinvention relates to a conjugate of generic formula:

Dideoxyxamatoxin-L-X*—S-Tbm,

wherein Dideoxyxamatoxin is an amatoxin according to the presentinvention, L is a linker, X* is a moiety resulting from coupling of athiol group to a thiol-reactive group, S is the sulphur atom of saidthiol group, particularly the thiol group of a cysteine amino acidresidue, and Tbm is a target-binding moiety, particularly an antibody ora functional antibody fragment comprising said cysteine amino acidresidue. In particular embodiments, said cysteine amino acid residue (i)is located in an antibody domain selected from CL, CH1, CH2, and CH3;(ii) is located at a position, where the germline sequence exhibitingthe closest homology to the sequence of said antibody domain contains anamino acid residue different from cysteine; and (iii) is located aposition that is solvent-exposed.

In the context of the present invention, the term “thiol-reactive group”refers to a group that selectively reacts with the thiol group of, forexample, a free cysteine of an antibody, particularly in a pH value inthe range between 6.0 and 8.0, more particularly in a pH value in therange between 6.5 and 7.5. In particular, the term “selectively” meansthat less than 10% of the coupling reactions of a molecule comprising athiol-reactive group with an antibody comprising at least one freecysteine residue are coupling reactions with non-cysteine residues ofthe antibody, such as lysine residues, particularly less than 5%, moreparticularly less than 2%. In particular embodiments, the thiol-reactivegroup is selected from bromoacetamide, iodoacetamide, maleimide, amaleimide having a leaving group in position 3, in particular a leavinggroup selected from —Br, and substituted thiol (see, for example, U.S.Pat. No. 9,295,729), a 1,2-dihydropyridazine-3,6-dione having a leavinggroup in position 4, in particular a leaving group selected from —Br,and substituted thiol (see, for example, U.S. Pat. No. 9,295,729),methylsulfonyl benzothiazole, methylsulfonyl phenyltetrazole,methylsulfonyl phenyloxadiazole (see Toda et al., Angew. Chem. Int. Ed.Engl., 52 (2013) 12592-6), a 3-arylpropionitrile (see Kolodych et al,Bioconjugate Chem. 2015, 26, 197-200), and5-nitro-pyridin-2-yl-disulfide ( . . . -L-S—S-(5-nitro-pyridine-2-yl).

In particular embodiments, said position or functional group, which ison one side connected to the linker and which can directly or indirectlybe connected to a position or functional group present in atarget-binding moiety is a moiety that can react with two thiol groupspresent in one target-binding moiety or in two target-binding moieties.In particular embodiments, the thiol-reactive groups is a maleimidehaving two leaving groups in positions 3 and 4, in particular selectedfrom 3,4-dibromomaleimide, 3,4-bis(arylthio)-maleimide, in particular3,4-diphenylthio-maleimide, and 3,4-bis(heteroarylthio)-maleimide, inparticular 3,4-bis(2-pyridinyl-sulfanyl)-maleimide, and. In particularother embodiments, the thiol-reactive groups is a1,2-dihydropyridazine-3,6-dione having two leaving groups in positions 4and 5, in particular selected from4,5-bromo-1,2-dihydropyridazine-3,6-dione,4,5-bis(arylthio)-1,2-dihydropyridazine-3,6-dione, in particular4,5-diphenylthio-1,2-dihydropyridazine-3,6-dione, and4,5-bis(heteroarylthio)-1,2-dihydropyridazine-3,6-dione, in particular4,5-bis(2-pyridinyl-sulfanyl)-1,2-dihydropyridazine-3,6-dione.

In particular embodiments, the moiety resulting from coupling of a thiolgroup to a thiol-reactive group is selected from: thiol-substitutedacetamide; thiol-substituted succinimide; thiol-substituted succinamicacid; thiol-substituded heteroaryl, particularly thiol-substitutedbenzothiazole, thiol-substituted phenyltetrazole and thiol-substitutedphenyloxadiazole; and a disulphide, wherein one sulphur atom is derivedfrom a cysteine residue of the antibody. In particular embodiments, themoiety resulting from coupling of a thiol group to a thiol-reactivegroup is a thiol-substituted succinimide.

In particular embodiments, the linker L in the moiety L-X*—S present inthe generic formula of section [0070], is selected from the followinggroup of moieties:

-   -   (dideoxyamatoxin side) —(CH₂)₂—S—S—(CH₂)₂—X—S— (Tbm side);    -   (dideoxyamatoxin side) —(CH₂)₃—S—S—(CH₂)₂—X—S— (Tbm side);    -   (dideoxyamatoxin side) —(CH₂)₂—S—S—(CH₂)₃—X—S— (Tbm side);    -   (dideoxyamatoxin side) —(CH₂)₃—S—S—(CH₂)₃—X—S— (Tbm side);    -   (dideoxyamatoxin side) —(CH₂)₄—S—S—(CH₂)₄—X—S— (Tbm side);    -   (dideoxyamatoxin side) —(CH₂)₂—CMe₂-S—S—(CH₂)₂—X—S— (Tbm side);    -   (dideoxyamatoxin side) —(CH₂)₂—S—S—CMe₂-(CH₂)₂—X—S— (Tbm side);    -   (dideoxyamatoxin side) —(CH₂)₃—S—S— (Tbm side);    -   (dideoxyamatoxin side) —CH₂—C₆H₄—NH-Cit-Val-CO(CH₂)₅—X—S— (Tbm        side)    -   (dideoxyamatoxin side) —CH₂—C₆H₄—NH-Ala-Val-CO(CH₂)₅—X—S— (Tbm        side);    -   (dideoxyamatoxin side) —CH₂—C₆H₄—NH-Ala-Val-CO(CH₂)₂—X—S— (Tbm        side);    -   (dideoxyamatoxin side) —CH₂—C₆H₄—NH-Ala-Phe-CO(CH₂)₂—X—S— (Tbm        side);    -   (dideoxyamatoxin side) —CH₂—C₆H₄—NH-Lys-Phe-CO(CH₂)₂—X—S— (Tbm        side);    -   (dideoxyamatoxin side) —CH₂—C₆H₄—NH-Cit-Phe-CO(CH₂)₂—X—S— (Tbm        side);    -   (dideoxyamatoxin side) —CH₂—C₆H₄—NH-Val-Val-CO(CH₂)₂—X—S— (Tbm        side);    -   (dideoxyamatoxin side) —CH₂—O₆H₄—NH-Ile-Val-CO(CH₂)₂—X—S— (Tbm        side);    -   (dideoxyamatoxin side) —CH₂—C₆H₄—NH-His-Val-CO(CH₂)₂—X—S— (Tbm        side);    -   (dideoxyamatoxin side) —CH₂—O₅H₄—NH-Met-Val-CO(CH₂)₂—X—S— (Tbm        side);    -   (dideoxyamatoxin side) —CH₂—C₆H₄—NH-Asn-Lys-CO(CH₂)₂—X—S— (Tbm        side); and    -   wherein —NH— and —CO— flanking the dipeptide sequences represent        amino and carbonyl moieties of the linker forming amide bonds to        the carboxy- and the amino-terminus of the dipeptide,        respectively.

In the context of the present invention, the term “a moiety resultingfrom coupling of a thiol group to a thiol-reactive group” refers to astructure that results from (i) the nucleophilic substitution of aleaving group Y present in a thiol-reactive group by the sulphur atom ofa cysteine residue, for example a bromo acetamide group, a iodoacetamide, a 4,6-dichloro-1,3,5-triazin-2-ylamino group, an alkylsulfoneor a heteroarylsulfone; (ii) the addition of the HS-group of a cysteineresidue to an activated double bond of a thiol-reactive group, forexample maleimide, or (iii) an disulfide exchange of an activateddisulfide or methanethiosulfonate with the sulphur atom of a cysteineresidue, for example with pyridine-2-thiol, 5-nitropyridine-2-thiol ormethanesulfinate as leaving group; or (iv) any other chemical reactionthat results in a stable bond between the sulphur atom of a cysteineresidue and a reactive moiety being part of the thiol-reactive group.

The primary moiety resulting from coupling of thiol group may beoptionally further derivatized, e.g. the succinimidyl thioetherresulting from a maleimide can be hydrolysed to succinamic acidthioethers of the following generic structures

In particular other embodiments, site-specific coupling can be achievedby reducing a disulfide bridge present in the target-binding moiety, andby reacting the two cysteine residues with a bridging moiety X* presentin a Dideoxyxamatoxin -L-X* construct (see Badescu et al. Bridgingdisulfides for stable and defined antibody drug conjugates. BioconjugateChemistry. 25 (2014) 1124-1136).

In a similar embodiment, site-specific coupling can be achieved byreducing a disulfide bridge present in the target-binding moiety, and byreacting the two cysteine residues with a bridging moiety X* present ina Dideoxyxamatoxin -L -X* construct, particularly wherein X* is

(see Bryden et al., Bioconjug Chem, 25 (2014) 611-617; Schumacher etal., Org Biomol Chem, 2014, 7261-7269)

In a particular other embodiment, coupling is achieved by regiospecificcoupling of an amino group present in the linker to a glutamine residuepresent in the target-binding moiety via a transaminase, particularly bycoupling to glutamine Q295 of an antibody.

In a particular embodiment, coupling is achieved by site-specificconjugation to target-binding moieties comprising N-glycan side chains.In particular, the N-glycan side chain can be degraded enzymatically,followed by trans-glycosylation with an azido-galactose. Using clickchemistry, such modified target-binding moiety can be coupled toappropriately modified constructs Dideoxyxamatoxin -L -X*, wherein X*is, for example, a dibenzo-cyclooctyne (DIBO) or an analogous moietycomprising a C—C triple bond. For example, a constructDideoxyxamatoxin-L-NH₂ can be coupled to DIBO-SE

by nucleophilic substitution of the hydroxy succinimide moiety. Theresulting DIBO-modified linker construct can then be coupled to theazido derivative mentioned above. In an alternative embodiment, thetarget-binding moiety can be modified by incorporation of a non-naturalamino acid that permits click-chemistry, in particular by incorporationof a para-azidomethyl-L-phenylalanine (pAMF).

In particular embodiments, the linker L in -L -X* is a linear chain ofat least 5, particularly at least 10, more particularly between 10 and20 atoms independently selected from C, O, N and S, particularly between10 and 18 atoms, more particularly between 10 and 16 atoms, and evenmore particularly between 10 and 15 atoms. In particular embodiments, atleast 60% of the atoms in the linear chain are C atoms. In particularembodiments, the atoms in the linear chain are linked by single bonds.

In alternative embodiments, the position or functional group, which candirectly or indirectly be connected to a position or functional grouppresent in a target-binding moiety, is not an ethynyl group, or, moregenerally, is not an alkynyl group, or is not a group that can bereacted with an 1,3 dipole in a 1,3-dipolar cycloaddition (clickchemistry).

In particular other embodiments, site-specific coupling of aDideoxyxamatoxin -L -X* construct to a target-binding moiety can beachieved by by incorporation of a non-natural amino acid comprising aketo group, in particular p-acetylphenylalanine (pAcPhe), into thetarget-binding moiety, and by reacting such modified target-bindingmoiety with a Dideoxyxamatoxin -L -X* construct, wherein X* is ahydroxylamine moiety.

In a further embodiment, a formyl group can be introduced byformylglycine generating enzyme (FGE), which is highly selective for acysteine group in a recognition sequence CxPxR to generate an aldehydetag. Such aldehyde tag can be reacted with an appropriate group X*present in a Dideoxyxamatoxin -L -X* construct, in particular wherein X*is

(see Agarwal et al., Bioconjugate Chem 24 (2013) 846-851).

In a second aspect, the present invention relates to a pharmaceuticalcomposition comprising the conjugate of the present invention.

In a third aspect, the present invention relates to a conjugate of thepresent invention for use in the treatment of cancer in a patient,particularly wherein the cancer is selected from the group consisting ofbreast cancer, pancreatic cancer, cholangiocarcinoma, colorectal cancer,lung cancer, prostate cancer, ovarian cancer, prostate cancer, stomachcancer, kidney cancer, malignant melanoma, leukemia, and malignantlymphoma.

As used herein, “treat”, “treating” or “treatment” of a disease ordisorder means accomplishing one or more of the following: (a) reducingthe severity of the disorder; (b) limiting or preventing development ofsymptoms characteristic of the disorder(s) being treated; (c) inhibitingworsening of symptoms characteristic of the disorder(s) being treated;(d) limiting or preventing recurrence of the disorder(s) in patientsthat have previously had the disorder(s); and (e) limiting or preventingrecurrence of symptoms in patients that were previously symptomatic forthe disorder(s).

As used herein, the treatment may comprise administering a conjugate ora pharmaceutical composition according to the present invention to apatient, wherein “administering” includes in vivo administration, aswell as administration directly to tissue ex vivo, such as vein grafts.

In particular embodiments, a therapeutically effective amount of theconjugate of the present invention is used.

A “therapeutically effective amount” is an amount of a therapeutic agentsufficient to achieve the intended purpose. The effective amount of agiven therapeutic agent will vary with factors such as the nature of theagent, the route of administration, the size and species of the animalto receive the therapeutic agent, and the purpose of the administration.The effective amount in each individual case may be determinedempirically by a skilled artisan according to established methods in theart.

In another aspect the present invention relates to pharmaceuticalcomposition comprising an amatoxin according to the present invention,or a conjugate of the present invention of an amatoxin with atarget-binding moiety, and further comprising one or morepharmaceutically acceptable diluents, carriers, excipients, fillers,binders, lubricants, glidants, disintegrants, adsorbents; and/orpreservatives.

“Pharmaceutically acceptable” means approved by a regulatory agency ofthe Federal or a state government or listed in the U.S. Pharmacopeia orother generally recognized pharmacopeia for use in animals, and moreparticularly in humans.

In particular embodiments, the pharmaceutical composition is used in theform of a systemically administered medicament. This includesparenterals, which comprise among others injectables and infusions.Injectables are formulated either in the form of ampoules or as socalled ready-for-use injectables, e.g. ready-to-use syringes orsingle-use syringes and aside from this in puncturable flasks formultiple withdrawal. The administration of injectables can be in theform of subcutaneous (s.c.), intramuscular (i.m.), intravenous (i.v.) orintracutaneous (i.c.) application. In particular, it is possible toproduce the respectively suitable injection formulations as a suspensionof crystals, solutions, nanoparticular or a colloid dispersed systemslike, e.g. hydrosols.

Injectable formulations can further be produced as concentrates, whichcan be dissolved or dispersed with aqueous isotonic diluents. Theinfusion can also be prepared in form of isotonic solutions, fattyemulsions, liposomal formulations and micro-emulsions. Similar toinjectables, infusion formulations can also be prepared in the form ofconcentrates for dilution. Injectable formulations can also be appliedin the form of permanent infusions both in in-patient and ambulanttherapy, e.g. by way of mini-pumps.

It is possible to add to parenteral drug formulations, for example,albumin, plasma, expander, surface-active substances, organic diluents,pH-influencing substances, complexing substances or polymericsubstances, in particular as substances to influence the adsorption ofthe target-binding moiety toxin conjugates of the invention to proteinsor polymers or they can also be added with the aim to reduce theadsorption of the target-binding moiety toxin conjugates of theinvention to materials like injection instruments orpackaging-materials, for example, plastic or glass.

The amatoxins of the present invention comprising a target-bindingmoiety can be bound to microcarriers or nanoparticles in parenteralslike, for example, to finely dispersed particles based onpoly(meth)acrylates, polylactates, polyglycolates, polyamino acids orpolyether urethanes. Parenteral formulations can also be modified asdepot preparations, e.g. based on the “multiple unit principle”, if thetarget-binding moiety toxin conjugates of the invention are introducedin finely dispersed, dispersed and suspended form, respectively, or as asuspension of crystals in the medicament or based on the “single unitprinciple” if the target-binding moiety toxin conjugate of the inventionis enclosed in a formulation, e.g. in a tablet or a rod which issubsequently implanted. These implants or depot medicaments in singleunit and multiple unit formulations often consist of so calledbiodegradable polymers like e.g. polyesters of lactic acid and glycolicacid, polyether urethanes, polyamino acids, poly(meth)acrylates orpolysaccharides.

Adjuvants and carriers added during the production of the pharmaceuticalcompositions of the present invention formulated as parenterals areparticularly aqua sterilisata (sterilized water), pH value influencingsubstances like, e.g. organic or inorganic acids or bases as well assalts thereof, buffering substances for adjusting pH values, substancesfor isotonization like e.g. sodium chloride, sodium hydrogen carbonate,glucose and fructose, tensides and surfactants, respectively, andemulsifiers like, e.g. partial esters of fatty acids of polyoxyethylenesorbitans (for example, Tween®) or, e.g. fatty acid esters ofpolyoxyethylenes (for example, Cremophor®), fatty oils like, e.g. peanutoil, soybean oil or castor oil, synthetic esters of fatty acids like,e.g. ethyl oleate, isopropyl myristate and neutral oil (for example,Miglyol®) as well as polymeric adjuvants like, e.g. gelatine, dextran,polyvinylpyrrolidone, additives which increase the solubility of organicsolvents like, e.g. propylene glycol, ethanol, N,N-dimethylacetamide,propylene glycol or complex forming substances like, e.g. citrate andurea, preservatives like, e.g. benzoic acid hydroxypropyl ester andmethyl ester, benzyl alcohol, antioxidants like e.g. sodium sulfite andstabilizers like e.g. EDTA.

When formulating the pharmaceutical compositions of the presentinvention as suspensions in a preferred embodiment thickening agents toprevent the setting of the target-binding moiety toxin conjugates of theinvention or, tensides and polyelectrolytes to assure theresuspendability of sediments and/or complex forming agents like, forexample, EDTA are added. It is also possible to achieve complexes of theactive ingredient with various polymers. Examples of such polymers arepolyethylene glycol, polystyrene, carboxymethyl cellulose, Pluronics® orpolyethylene glycol sorbit fatty acid ester. The target-binding moietytoxin conjugates of the invention can also be incorporated in liquidformulations in the form of inclusion compounds e.g. with cyclodextrins.In particular embodiments dispersing agents can be added as furtheradjuvants. For the production of lyophilisates scaffolding agents likemannite, dextran, saccharose, human albumin, lactose, PVP or varietiesof gelatine can be used.

In a fourth aspect, the present invention relates to a constructcomprising (a) an amatoxin comprising (i) an amino acid 4 with a6′-deoxy position; and (ii) an amino acid 8 with an S-deoxy position;and (c) a linker moiety carrying a reactive group for linking saidamatoxin to a target-binding moiety.

In a particular embodiment, the present invention relates to a constructhaving structure II

wherein:

-   -   R² is S;    -   R³ is selected from NHR⁵, —NH—OR⁵, and OR⁵;    -   R⁴ is H; and    -   wherein one of R⁵ is -L-Y, wherein L is a linker, and Y is a        reactive group for linking said construct to a target-binding        moiety.

EXAMPLES

In the following, the invention is explained in more detail bynon-limiting examples:

1. Synthesis of Synthetic Dideoxy Precursor Molecule K

The synthesis of the dideoxy precursor molecule K is described in WO2014/009025 in Example 5.5.

Compound K may be deprotected by treatment with 7 N methanolic NH₃solution (3.0 ml) and stirring overnight.

2. Synthesis of Synthetic Dideoxy Precursor HDP 30.2105

An alternative dideoxy precursor molecules comprising a —COOH groupinstead of the carboxamide group at amino acid 1 can be synthesized (HDP30.1895) and deprotected to result in HDP 30.2105.

Step 1: 4-Hydroxy-pyrrolidine-1,2-dicarboxylic acid 2-allyl ester1-(9H-fluoren-9-ylmethyl) ester (HDP 30.0013)

FmocHypOH (10.0 g, 28.3 mmol) was suspended in 100 ml 80% MeOH andCs2CO3 (4.6 g, 14.1 mmol) was added. The suspension was stirred at 50°C. for 30 minutes until complete dissolution. The reaction mixture wasconcentrated to dryness and resolved in 100 ml DMF. Allylbromide (1.6ml, 3.6 g, 29.7 mmol) was added dropwise and the reaction was stirredover night at RT. DMF was distilled off and the residue dissolved intert-butylmethyl ether. Precipitates were filtered and the clearsolution was absorbed on Celite prior column chromatography. Thecompound was purified on 220 g Silicagel with an n-hexane/ethyl acetategradient.

Yield: 11.5 g, 100%

Step 2: Resin Loading (HDP 30.0400)

HDP 30.0013 (5.0 g, 14.1 mmol), pyridinium 4-toluenesulfonate (1.33 g,5.3 mmol) were added to a suspension of1,3-dihydro-2H-pyran-2-yl-methoxymethyl resin (5.0 g, 1.0 mmol/gTHP-resin) in 40 ml dichloroethane. The reaction was stirred at 80° C.overnight. After cooling the resin was filtered and extensively washedwith dichloroethane, dimethylformamide, acetonitrile, dichloromethaneand tert-butylmethylether Loading was 0.62 mmol/g (determined byUV-spectroscopy of the fluorene methyl group after deprotection)

Step 3: Solid Phase Precursor Synthesis (HDP 30.1894)

Resin Pre-Treatment:

HDP 30.0400 (0.5 g, 0.31 mmol) was treated with N,N-dimethylbarbituricacid (483 mg, 3.1 mmol) and Pd(PPh3)4 (69 mg, 0.06 mmol). The resin wasshaken over night at RT. Thereafter the resin was extensively washedwith dichloromethane, N-methyl-2-pyrrolidone, acetonitrile,dichloromethane and tert-butylmethyl ether and dried under reducedpressure.

Coupling Procedure:

All reactants and reagents were dissolved indichloromethane/N-methyl-2-pyrrolidone containing 1% Triton-X100(Solvent A).

HDP 30.0477 (257 mg, 0.38 mmol) was dissolved in 3.0 ml Solvent A andtreated with 3.0 ml of a 0.2 N solution PyBOP (333 mg, 0.63 mmol, 2.0eq), 3.0 ml of a 0.2 N solution HOBt (130 mg, 0.63 mmol, 2.0 eq) and 439μl DIEA (4.0 eq). The reaction was heated to 50° C. for 8 minutes bymicrowave irradiation (20 W, CEM microwave reactor) and was washed withN-methyl-2-pyrrolidone after coupling.

Deprotection:

Deprotection was performed by addition of 6.0 ml 20% piperidine inN-methyl-2-pyrrolidone at 50° C. for 8 minutes. The resin was washedwith N-methyl-2-pyrrolidone.

(Note: No deprotection after coupling of the final amino acid)

All other amino acids were coupled following the above protocol,weightings are shown below:

0.63 mmol, 498 mg Fmoc Asp(OAlI)OH0.63 mmol, 738 mg Fmoc Cys(Tri)OH0.63 mmol, 375 mg Fmoc GlyOH0.63 mmol, 445 mg FmocIleOH0.63 mmol, 375 mg Fmoc GlyOH0.38 mmol, 242 mg N-Boc-HPIOH (HDP 30.0079)

4,5-Diacetoxy-2-amino-3-methyl-pentanoic acid tert-butyl ester;hydrochloride (HDP 30.0477) was synthesized as described in WO2014/009025.

N-Boc-HPIOH (HDP 30.0079) was prepared according to Zanotti, Giancarlo;Birr Christian; Wieland Theodor; International Journal of Peptide &Protein Research 18 (1981) 162-8.

Step 4: HDP 30.1895

Elimination from Resin and B-Ring Formation

The resin was shaken with 10 ml trifluoroacetic acid containing 5%triisopropylsilane for 30 min and finally eluted into a 50 ml flask. Theresin was washed twice with methanol (10 ml each). The combined eluateswere concentrated in vacuum and re-suspended in 2-4 ml methanol. Themethanolic solution was dropped twice into 50 ml cold diethyl ether forpeptide precipitation. After centrifugation the precipitate was washedwith diethyl ether (2 times) and dried under reduced pressure. The whiteprecipitate was solubilized in approx. 4-5 ml methanol (0.5 ml per 100mg) and purified by preparative reverse phase column chromatography.Approximately 100 mg crude precipitate were purified per run. Fractionswere analyzed by mass spectrometry, combined and methanol distilled offunder reduced pressure. The aqueous phase was freeze dried.

Yield: 24.4 mg, 23.7 μmol

Mass spectrometry: [M+H]⁺, 1030.5

A-Ring Formation

The above freeze dried intermediate was dissolved in 25 mldimethylformamide and treated with diphenylphosphorylazide (63 μl, 1185μmol, 5 eq) and diisopropylethyl amine (201 μl, 1185 μmol, 5 eq). Thereaction was stirred overnight (20 hours). Conversion was monitored byreverse phase chromatography and finally quenched with 100 μl water. Themixture was concentrated by reduced pressure and re-dissolved in 1-2 mlmethanol. Precipitation of the product was performed by dropwiseaddition to 20 ml diethyl ether. The precipitate was washed twice withdiethyl ether and dried under reduced pressure. The next step wasperformed without further purification.

Mass spectrometry: [M+Na]⁺, 1034.6

Ester Deprotection:

To the crude cyclisation product 2.5 ml dichloromethane,diethylbarbituric acid (22.3 mg, 118.5 μmol) and Pd(PPh₃)₄ (27 mg, 23.7μmol) were added. The reaction was stirred at RT overnight. The reactioncan be monitored by RP-HPLC. After complete conversion, the mixture wasadded dropwise to 20 ml cooled diethyl ether and the precipitate washedtwice with diethyl ether. After drying at reduced pressure theprecipitate was dissolved in methanol (1.0 ml) and purified bypreparative reversed phase chromatography.

Yield: 15.0 mg

Mass spectrometry: [M+H]⁺, 972.3; [M+Na]⁺, 994.5

Step 5: HDP 30.2105

HDP 30.1895 (15.0 mg, 15.3 μmol) was dissolved in 7 N methanolic NH₃solution (3.0 ml) and stirred overnight. Conversion was checked by massspectrometry. After complete conversion the reaction was concentrated invacuum, suspended in 80% tert-butanol and lyophilized. Product waspurified by preparative HPLC.

Yield: 12.1 mg

Mass spectrometry: [M+H]⁺, 888.0; [M+Na]⁺, 910.2

3. Synthesis of Synthetic Dideoxy Precursor HDP 30.2115

A dideoxy precursor molecule comprising a thiol reactive group withcleavable linker can be synthesized from example 2 product in 7 steps asfollows:

Step 1: Fmoc-Val-OSu (HDP 30.1343)

This compound is prepared according to R. A. Firestone et al, U.S. Pat.No. 6,214,345. Fmoc-Val-OH (20.24 g; 59.64 mmol) andN-hydroxysuccinimide (6.86 g=1.0 eq.) in tetrahydrofuran (200 ml) at 0°C. were treated with N,N′-dicyclohexylcarbodiimide (12.30 g; 1.0 eq.).The mixture was stirred at RT under argon atmosphere for 6 h and thenthe solid dicyclohexyl urea (DCU) by-product was filtered off and washedwith THF and the solvent was removed by rotavap. The residue wasdissolved in 300 ml dichloromethane, cooled in an ice bath for 1 h andfiltered again to remove additional DCU. The dichloromethane wasevaporated and the solid foam (26.51 g) was used in the next stepwithout further purification.

Step 2: Fmoc-Val-Ala-OH (HDP 30.1414)

Step 2 product is prepared in analogy to P. W. Howard et al. US2011/0256157. A solution of L-alanine (5.58 g; 1.05 eq.) and sodiumhydrogen carbonate (5.51 g; 1.1 eq.) in 150 ml water was prepared andadded to a solution of HDP 30.1343 (26.51 g; max. 59.6 mmol) in 225 mltetrahydrofuran. The mixture was stirred for 50 h at RT. Afterconsumption of starting material the solution was partitioned between240 ml of 0.2 M citric acid and 200 ml of ethyl acetate. The aqueouslayer was separated and extracted with ethyl acetate (3×200 ml). Thecombined organic layers were washed with water and brine (300 ml each)dried (MgSO₄) and the solvent was evaporated to approx. 200 ml. Pureproduct precipitated at this time and was filtered off. The motherliquor was evaporated to dryness and the residue was stirred 1 h with100 ml MTBE to result additional crystalline material. The two crops ofproduct were combined to 18.01 g (74%) white powder. (m.p.: 203-207° C.)

MS (ESI+) [M+Na]⁺ found: 410.94; calc.: 411.19 (C₂₃H₂₇N₂O₅)

-   -   [M+Na]⁺ found: 433.14; calc: 433.17 (C₂₃H₂₇N₂O₅)    -   [2M+H]⁺ found: 842.70; calc.: 843.36 (C₄₆H₅₂N₄NaO₁₀)

Step 3: Fmoc-Val-Ala-PAB-NHBoc (HDP 30.1713)

Step 2 product HDP 30.1414 (1.76 g; 4.28 mmol) and4-[(N-Boc)aminomethyl]aniline (1.00 g; 1.05 eq.) were dissolved in 26 mlabs. tetrahydrofuran. 2-Ethoxy-N-(ethoxycarbonyl)-1,2-dihydroquinoline(EEDQ 1.11 g; 1.05 eq.) was added and the mixture was stirred at RT,protected from light. With ongoing reaction a gelatinous matter isformed from the initially clear solution. After 40 h the reactionmixture was diluted with 25 ml of tert-butylmethyl ether (MTBE) andstirred for 1 h. Subsequently the precipitation is filtered off withsuction, washed with MTBE and dried in vacuo to 2.30 g (85% yield) of awhite solid.

¹H NMR (500 MHz, DMSO-d6) δ 9.87 (s, 1H), 8.11 (d, J=7.1 Hz, 1H), 7.88(d, J=7.5 Hz, 2H), 7.74 (q, J=8.4, 7.9 Hz, 2H), 7.51 (d, J=8.2 Hz, 2H),7.45-7.23 (m, 7H), 7.17 (d, J=8.3 Hz, 2H), 4.44 (p, J=7.0 Hz, 1H),4.36-4.17 (m, 3H), 3.96-3.89 (m, 1H), 2.01 (hept, J=6.9 Hz, 1H), 1.39(s, 9H), 1.31 (d, J=7.1 Hz, 3H), 0.90 (d, J=6.8 Hz, 3H), 0.87 (d, J=6.8Hz, 3H).

¹³C NMR (126 MHz, DMSO-d6) δ 170.84, 170.76, 156.04, 155.63, 143.77,143.69, 140.60, 137.41, 134.99, 127.50, 127.26, 126.93, 125.22, 119.95,118.97, 77.60, 65.62, 59.95, 48.86, 46.62, 42.93, 30.28, 28.16, 19.06,18.10, 18.03.

Step 4: H-Val-Ala-PAB-NHBoc (HDP 30.1747)

Step 3 compound HDP 30.1713 (1.230 g, 2.00 mmol) was placed in a 100 mlflask and dissolved in 40 ml dimethylformamide (DMF). Diethyl amine (7.5ml) was added and the mixture was stirred at RT. The reaction wasmonitored by TLC (chloroform/methanol/HOAc 90:8:2). After consumption ofstarting material (30 min) the volatiles were evaporated and the residuewas co-evaporated with 40 ml fresh DMF to remove traces of diethylamine. The crude product was used without further purification for thenext step.

MS (ESI+) [MH]⁺ found: 393.26; calc.: 393.25 (C₂₀H₃₃N₄O₄)

-   -   [M+Na]⁺ found: 415.35; calc.: 415.23 (C₂₀H₃₂N₄NaO₄)    -   [2M+H]⁺ found: 785.37; calc.: 785.49 (C₄₀H₆₅N₈O₈)

Step 5: B P-Val-Ala-PAB-NHBoc (HDP 30.2108)

Crude step 4 product HDP 30.1747 (max 2.00 mmol) was dissolved in 40 mlDMF, 3-(maleimido)propionic acid N-hydroxysuccinimide ester (BMPS 532mg; 1.0 eq.) and N-ethyldiisopropylamine (510 μl, 1.5 eq.) were addedand the mixture was stirred 3 h at RT After consumption of startingmaterial HDP 30.1747 (TLC: chloroform/methanol/HOAc 90:8:2) thevolatiles were evaporated and the residue is stirred with 50 ml MTBEuntil a fine suspension was formed (1 h). The precipitate was filteredoff with suction, washed with MTBE and dried. The crude product (1.10 g)was dissolved in 20 ml dichloromethane/methanol 1:1, kieselgur (15 g)was added and the solvents were stripped off. The solid material wasplaced on top of an 80 g silica gel column and eluted with a lineargradient of 0-10% methanol in dichloromethane. Product fractions werecombined and evaporated to 793 mg (73% over two steps) amorphous solid.

MS (ESI⁺) [M+Na]⁺ found: 566.24; calc.: 566.26 (C₂₇H₃₇N₅NaO₇)

¹H NMR (500 MHz, DMSO-d₆) δ 9.75 (s, 1H), 8.09 (d, J=7.1 Hz, 1H), 7.98(d, J=8.4 Hz, 1H), 7.52 (d, J=8.6 Hz, 2H), 7.29-7.23 (m, 1H), 7.16 (d,J=8.5 Hz, 2H), 6.98 (s, 2H), 4.39 (p, J=7.1 Hz, 1H), 4.13 (dd, J=8.4,6.7 Hz, 1H), 4.06 (d, J=6.1 Hz, 2H), 3.67-3.56 (m, 2H), 2.49-2.41 (m,2H), 1.96 (h, J=6.8 Hz, 1H), 1.39 (s, 9H), 1.30 (d, J=7.1 Hz, 3H), 0.86(d, J=6.8 Hz, 3H), 0.82 (d, J=6.8 Hz, 3H).

¹³C NMR (126 MHz, DMSO-d₆) δ 170.80, 170.63, 170.60, 169.72, 155.65,137.45, 134.94, 134.44, 127.26, 118.95, 77.62, 57.71, 48.92, 42.95,33.96, 33.64, 30.17, 28.17, 19.02, 18.06, 17.82.

Step 6: B P-Val-Ala-PAB-NH₂ (HDP 30.2109)

Step 5 product HDP 30.2108 (400 mg, 736 μmol) was dissolved in 4,000 μltrifluoroacetic acid and stirred for 2 min. Subsequently the volatileswere evaporated at RT and the remainders were co-evaporated twice with4,000 μl toluene. The residue was dissolved in 5,000 μl1,4-dioxane/water 4:1, solidified in liquid nitrogen and freeze-dried:410 mg (quant.) colorless powder

MS (ESI+) [M+Na]⁺ found: 415.35; calc.: 466.21 (C₂₂H₂₉N₅NaO₅)

-   -   [2M+H]⁺ found: 887.13; calc.: 887.44 (C₄₄H₅₉N₁₀O₁₀)

¹H NMR (500 MHz, DMSO-d₆) δ 9.89 (s, 1H), 8.13 (d, J=6.9 Hz, 1H), 7.99(d, J=8.2 Hz, 1H), 7.66-7.60 (m, 2H), 7.41-7.34 (m, 2H), 6.98 (s, 2H),4.39 (p, J=7.1 Hz, 1H), 4.11 (dd, J=8.2, 6.6 Hz, 1H), 3.97 (q, J=5.6 Hz,2H), 3.69-3.58 (m, 2H), 2.49-2.40 (m, 2H), 1.96 (h, J=6.8 Hz, 1H), 1.32(d, J=7.1 Hz, 3H), 0.86 (d, J=6.8 Hz, 3H), 0.83 (d, J=6.7 Hz, 3H).

¹³C NMR (126 MHz, DMSO-d₆) δ 171.24, 170.78, 170.72, 169.85, 158.12 (q,J=33.2 Hz, TEA), 158.25, 157.99, 157.73, 139.19, 134.53, 129.45, 128.52,119.02, 116.57 (q, J=296.7 Hz, TFA), 57.78, 49.08, 41.90, 34.00, 33.68,30.21, 19.07, 18.16, 17.76.

Step 6: HDP 30.2115

HDP 30.2105 (15.0 mg, 16.5 μmol) were treated with 429 μl of a 0.1 Msolution of HDP 30.2109 (25.2 μmol, 1.5 eq), 492 μl of 0.1 M TBTU (25.2μmol, 1.5 eq) and 492 μl of 0.2 M DIEA (49.1 μmol, 3.0 eq) at RT. Thereaction was monitored by RP-HPLC. After completion the reaction wasquenched with 100 μl H₂O stirred for 15 minutes and injected onto apreparative RP-HPLC.

Yield: 12.2 mg, 56%

Mass spectrometry: 1313.2 [M+H]⁺, 1335.5 [M+Na]⁺

4. Synthesis of Synthetic Dideoxy Precursor HDP 2179 4.1 Synthesis ofHDP 30.2179

4.2 Synthesis of HDP 30.2007

770.0 mg (1.96 mmol) HDP 30.1960, prepared according to EP 15 000 681.5,319.2 mg (1.96 mmol) N-hydroxyphthalimide and 513.3 (1.96 mmol)triphenylphosphine were dissolved in 40 ml dry tetrahydrofuran. Underargon 889.2 μl (1.96 mmol) of an ethyl diazocarboxylate solution intoluene (40%) were added over 30 min. The reaction mixture was stirredfor 24 h at RT and evaporated to dryness. The solid residue was purifiedon a silica-gel-column with a gradient from CHCl₃ to CHCl₃/MeOH (30/1)as eluent. Crude HDP 30.2007 was obtained as a yellow solid. The crudeproduct was further purified on a silica-gel-column with a gradient fromn-hexane to n-hexane/ethyl acetate/methanol (10/10/1) as eluent. HDP30.2007 was obtained as a white solid. Yield: 270.0 mg (22%).

MS (ESI⁺) found: 561.14 [M+Na]⁺, calc.: 561.24 (C₂₈H₃₄N₄NaO₇)

MS (ESI⁺) found: 1099.70 2 [M+Na]⁺; calc.: 1099.48 (C₅₆H₆₈N₈NaO₁₄)

4.3 Synthesis of HDP 30.2011

270.0 mg (0.50 mmol) HDP 30.2007 was suspended in 16 ml dichloromethane.Under argon, 50.3 μl (1.04 mmol) hydrazine hydrate was added at once andthe reaction mixture stirred for 24 h under argon and RT. The suspensionwas filtered and the solid washed with dichloromethane. The filtrateswere evaporated and the residue dried in high vacuum. HDP 30.2011 wasobtained as a white solid and was used for the next steps withoutfurther purification. Yield: 199.0 mg (97%).

MS (ESI⁺) found: 431.50 [M+Na]⁺; calc.: 431.24 (C₂₀H₃₂N₄NaO₅)

4.4 Synthesis of HDP 30.2177

20.59 mg (23.17 μmol) HDP 30.2105 was dissolved in 1,200 ml drydimethylformamide (DMF). The solution was purged with argon and treatedwith 18.85 mg (46.10 μmol) HDP 30.2011 dissolved in drydimethylformamide (DMF), 24.05 mg (46.10 μmol) PyBOP(benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate)dissolved in 450 ml dry dimethylformamide (DMF) and 86.20 μl (82.30mmol)N-ethyl-diisopropylamine (DIPEA) solution in DMF (100 μl DIPEAdissolved in 500 μl DMF). The reaction mixture was stirred at RT underargon. After 5 h the reaction volume was diluted with coldmethyl-t-butylether (MTBE). The white precipitate was centrifuged andwashed with cold MTBE. The crude solid was purified by RP18 HPLC (Luna™10μ, 250×21 mm, Phenomenex®, 290 nm) with a gradient of 95% H₂O/5% MeOHto 95% MeOH/5% H₂O and a flow rate of 15 ml/min. The product fraction at17.5 min was collected, evaporated and freeze dried in water to 13.84 mg(47%) HDP 30.2177 as a white, amorphous solid.

MS (ESI⁺) found: 1278.45 [MH]⁺; calc.: 1277.58 (C₅₉H₈₃N₁₃O₁₇S)

MS (ESI⁺) found: 1300.84 [M+Na]⁺; calc.: 1300.58 (C₅₉H₈₃N₁₃NaO₁₇S)

4.5 Synthesis of HDP 30.2179

13.84 mg (10.82 μmol) HDP 30.2177 was dissolved in 2,000 μltrifluoroacetic acid (TFA) and stirred for 5 minutes at RT. Excess TFAwas removed with a rotary evaporator at 33° C. water bath temperatureand the remaining residue treated with 5 ml of methanol and evaporatedto dryness. The oily residue was dried in high vacuum, forming a whitesolid. The solid was dissolved in 1,700 μl dry dimethylformamide (DMF)and treated with 5.77 mg (21.67μmol)N-Succinimidyl-3-Maleimidopropionate (BMPS). 75.40 μl DIPEAsolution (50 μl DIPEA dissolved in 450 μl dry DMF) was added. Thereaction mixture was stirred under argon for 5 h and treated with 20 mlof cold MTBE. The precipitate was centrifuged, washed with cold MTBE anddried. The crude product was purified by RP18 HPLC (Luna™ 10μ, 250×21mm, Phenomenex®, 290 nm) with a gradient of 95% H₂O/5% MeOH to 95%MeOH/5% H₂O and a flow rate of 15 ml/min. The product fraction at 14.5minutes was collected, evaporated and freeze dried in water to yield7.40 mg (51%) HDP 30.2179 as a white, amorphous solid.

MS (ESI⁺) found: 1351.50 [M+Na]⁺; calc.: 1351.55 (C₆₁H₈₀N₁₄NaO₁₈S)

Furthermore, an alternative dideoxy precursor molecule comprising a—CO—NHOH group instead of the carboxamide group at amino acid 1 can besynthesized for example by reacting the carboxylate precursor HDP30.2105 with O-benzyl hydroxylamine under standard condensationconditions (PyBOP, DCC, mixed anhydride etc.). The benzylic group of theso obtained O-benzyl hydroxamic acid derivative of HDP 30.2105 caneasily be removed under catalytic hydrogenolytic conditions (Pd/H2),forming the free —CO—NHOH group. This acidic hydroxamic function canthen be alkylated to —CO—NHOR with different halogenated or O-tosylatedalkyl-linker building blocks. This alkylation takes place under basicconditions with LiOH, NaOH, KO-t-Bu or other suitable bases.

5. Synthesis of Synthetic Dideoxy Precursor HDP 30.2191

A dideoxy precursor molecule comprising a thiol reactive group withstable linker can be synthesized from example 2 product as follows:

Example 2 product (HDP 30.2105), 11.00 mg (12.39 μmol) was dissolved in123.9 μl dry DMF. Subsequently 1 M solutions of N-hydroxysuccinimide anddiisopropylcarbodiimide in DMF (123.9 μl, 10 eq. each) were added. After1 h at RT a 1 M solution of N-(2-aminoethyl)maleimide trifluoroacetatesalt in DMF was added and the reaction mixture was stirred foradditional 4 h. Then the reaction mixture was dropped in 10 ml of MTBEat 0° C. The resulting precipitate was collected by centrifugation andwashed with additional 10 ml of MTBE. The residue was purified bypreparative HPLC on a C18 column with a gradient from 5-100% methanol.The product containing fractions evaporated and lyophilized fromt-butanol/water to result 9.27 mg (54%) title compound as colorlesspowder

MS (ESI+) [MH]⁺ found: 1010.3; calc.: 1010.4 (C₄₅H₆₀N₁₁O₁₄S)

-   -   [M+Na]⁺ found: 1032.5; calc.: 1032.39 (C₄₅H₅₉N₁₁NaO₁₄S)

6. Synthesis of Synthetic Dideoxy Precursor HDP 30.2157

A dideoxy precursor molecule comprising a thiol reactive group withreducible linker can be synthesized from example 2 product as follows:

Step 1:

Example 2 product (HDP 30.2105), 11.36 mg (12.97 μmol) is dissolved in512 μl dry DMF. Subsequently A 0.1M solutions of PyBOP in DMF (512 μl, 4eq.) and 8.70 μl (4 eq.) DIPEA were added. After 1 min a 0.1M solutionof 3-[(triphenylmethyl)sulfanyl]propan-1-amine in dichloromethane isadded and the reaction mixture was stirred for additional 3.5 h. Thenthe reaction mixture was dropped in 10 ml of MTBE at 0° C. The resultedprecipitate was collected by centrifugation and washed with additional10 ml of MTBE. The residue was purified by preparative HPLC on a C18column with a gradient from 5-100% methanol. The product containingfractions evaporated and lyophilized from t-butanol/water 4:1 to result9.52 mg (62%) product as amorphous solid.

MS (ESI+) [M+Na]⁺ found: 1225.30; calc.: 1225.48 (C₆₁H₇₄N₁₀NaO₁₂S₂)

Step 2:

To step 1 product (9.52 mg, 7.91 μmol) a 0.5 M solution of2,2′-dithiobis(5-nitropyridine), DTNP in trifluoroacetic acid (79.1 μl,5 eq.) was added. After 4 min the reaction mixture was precipitated in10 ml of MTBE at 0° C. The resulting solids were collected bycentrifugation and washed with additional 10 ml of MTBE. The crudeproduct was purified by preparative HPLC on a C18 column with a gradientfrom 5-100% methanol with 0.05 TFA. The pure fraction was evaporated andthe residue lyophilized from 2 ml t-butanol/water 4:1 to give 7.48 mg(85%) HDP 30.2157 as a slightly yellowish powder.

MS (ESI⁺) 1146.97 [M+H]⁺, 1169.17 [M+Na]⁺

7. Synthesis of Conjugate chiBCE19-D265C-30.2115

Conjugation of HDP 30.2115 to 10 mg chiBCE19-D265C

10 mg Thiomab chiBCE19-D265C in PBS buffer will be used for conjugationto HDP 30.2115.

Adjust antibody solution to 1 mM EDTA:

2 ml antibody solution (10.0 mg)+20 μl 100 mM EDTA, pH 8.0

Amount antibody: 10 mg=6.8×10⁻⁸ mol

Uncapping of cysteines by reaction of antibody with 40 eq. TCEP:

-   -   2 ml antibody solution (6.8×10⁻⁸ mol)+54.5 μl 50 mM TCEP        solution (2.72×10⁻⁶ mol)    -   Incubate for 3 h at 37° C. on a shaker.    -   Two consecutive dialyses at 4° C. in 2.0 l 1×PBS, 1 mM EDTA, pH        7.4 in a Slide-A-Lyzer Dialysis Cassette 20,000 MWCO, first        dialysis ca. 4 h, second dialysis overnight    -   Concentrate to ca. 4.0 ml using Amicon Ultra Centrifugal Filters        50,000 MWCO.        Oxidation by reaction of antibody with 20 eq. dehydroascorbic        acid (dhAA):    -   ca. 2 ml antibody solution (6.8×10⁻⁸ mol)+27.2 μl fresh 50 mM        dhAA solution (1.36×10⁻⁶ mol)    -   Incubate for 3 h at RT on a shaker.        Conjugation with amanitin using 6 eq. HDP 30.2115 and quenching        with 25 eq. N-acetyl-L-cysteine:

Solubilize 0.7 mg HDP 30.2115 in 70 μl DMSO=10 μg/μl

-   -   ca. 2 ml antibody solution (=9.5 mg; 6.46×10⁻⁸ mol)+50.9 μl HDP        30.2115 (=509 μg; 3.88×10⁻⁷ mol).    -   Incubate 1 h at RT.    -   Quench by addition of 16 μl 100 mM N-acetyl-L-cysteine        (1.62×10⁻⁶ mol).    -   Incubate 15 min at RT (or overnight at 4° C.).    -   Purify each reaction mix with PD-10 columns equilibrated with        1×PBS, pH 7.4. Identify protein-containing fractions with        Bradford reagent on parafilm and bring protein-containing        fractions together.    -   Dialysis of each antibody solution at 4° C. overnight in 2.0 l        PBS, pH 7.4 and Slide-A-Lyzer Dialysis Cassettes 20,000 MWCO.        Determination of protein concentration and drug-antibody ratio        (DAR) by UV-spectra (absorption at 280 nm and 310 nm) using        naked antibody vs. ADC adjusted to identical protein        concentrations.        Adjust protein concentration to 5.0 mg/ml (3.4×10⁻⁵M) and bring        to sterile conditions by filtration. Store at 4° C.

8. Synthesis of Conjugate chiBCE19-D265C-30.2179

Conjugation of HDP 30.2179 to 10 mg chiBCE19-D265C

10 mg of the Thiomab chiBCE19-D265C in PBS buffer will be used forconjugation to HDP 30.2179.

Adjust antibody solution to 1 mM EDTA:

2 ml antibody solution (10.0 mg)+20 μl 100 mM EDTA, pH 8.0

Amount antibody: 10 mg=6.8×10⁻⁸ mol

Uncapping of cysteines by reaction of antibody with 40 eq. TCEP:

-   -   2 ml antibody solution (6.8×10⁻⁸ mol)+54.5 μl 50 mM TCEP        solution (2.72×10⁻⁶ mol)    -   Incubate for 3 h at 37° C. on a shaker.    -   Two consecutive dialyses at 4° C. in 2.0 l 1×PBS, 1 mM EDTA, pH        7.4 in a Slide-A-Lyzer Dialysis Cassette 20,000 MWCO, first        dialysis ca. 4 h, second dialysis overnight    -   Concentrate to ca. 4.0 ml using Amicon Ultra Centrifugal Filters        50,000 MWCO.        Oxidation by reaction of antibody with 20 eq. dehydroascorbic        acid (dhAA):    -   ca. 2 ml antibody solution (6.8×10⁻⁸ mol)+27.2 μl fresh 50 mM        dhAA solution (1.36×10⁻⁶ mol)    -   Incubate for 3 h at RT on a shaker.        Conjugation with amanitin using 6 eq. HDP 30.2179 and quenching        with 25 eq. N-acetyl-L-cysteine:

Solubilize 0.7 mg of HDP 30.2179 in 70 μl DMSO=10 μg/μl

-   -   ca. 2 ml antibody solution (=9.5 mg; 6.46×10⁻⁸ mol)+51.5 μl HDP        30.2179 (=515 μg; 3.88×10⁻⁷ mol).    -   Incubate 1 h at RT.    -   Quench by addition of 16 μl 100 mM N-acetyl-L-cysteine        (1.62×10⁻⁶ mol).    -   Incubate 15 min at RT (or overnight at 4° C.).    -   Purify each reaction mix with PD-10 columns equilibrated with        1×PBS, pH 7.4. Identify protein-containing fractions with        Bradford reagent on parafilm and bring protein-containing        fractions together.    -   Dialysis of each antibody solution at 4° C. overnight in 2.0 l        PBS, pH 7.4 and Slide-A-Lyzer Dialysis Cassettes 20,000 MWCO.

Determination of protein concentration and drug-antibody ratio (DAR) byUV-spectra (absorption at 280 nm and 310 nm) using naked antibody vs.ADC adjusted to identical protein concentrations.

Adjust protein concentration to 5.0 mg/ml (3.4×10⁻⁵M) and bring tosterile conditions by filtration. Store at 4° C.

9. Conjugation of HDP 30.2115 to 30 mg DIG-D265C

30 mg of cysteine engineered antibody in PBS at 5.0 mg/ml will be usedfor conjugation to HDP 30.2115

-   -   Adjust antibody solution to 1 mM EDTA:    -   6 ml antibody solution (30 mg)+60 μl 100 mM EDTA, pH 8.0    -   Amount antibody: 2.05×10⁻⁷ mol        Uncapping of cysteines by reaction of antibody with 40 eq. TCEP:    -   6 ml antibody solution (2.05×10⁻⁷ mol)+164 μl 50 mM TCEP        solution (8.21×10⁻⁶ mol)    -   Incubate for 3 h at 37° C.    -   Purify each antibody from TCEP by two consecutive dialyses at        4° C. in 2.0 l 1× PBS, 1 mM EDTA, pH 7.4 in a Slide-A-Lyzer        Dialysis Cassette 20,000 MWCO, first dialysis ca. 4 h, second        dialysis overnight.        Oxidation by reaction of antibody with 20 eq. dehydroascorbic        acid (dhAA):    -   ca. 6 ml antibody solution (2.05×10⁻⁷ mol)+82 μl fresh 50 mM        dhAA solution (4.1×10⁻⁶ mol)    -   Incubate for 3 h at RT.        Conjugation with amanitin using 6 eq. HDP 30.2115 and quenching        with 25 eq. N-acetyl-L-cysteine:

Solubilize 2.0 mg HDP 30.2115 in 200 μl DMSO=10 μg/μl

-   -   ca. 6 ml antibody solution (=ca. 29 mg; 1.98×10⁻⁷ mol)+156 μl        HDP 30.2115 (=1563 μg; 1.19×10⁻⁶ mol).    -   Incubate 1 h at RT.    -   Quench by addition of 49.6 μl 100 mM N-acetyl-L-cysteine        (4.96×10⁻⁶ mol).    -   Incubate 15 min at RT (or overnight at 4° C.).    -   Centrifuge at full speed for app. 3 min, take supernatant and        measure volume exactly for preparative FPLC.    -   Purify each reaction mix by preparative FPLC (ÄKTA) using HiLoad        16/600-Superdex 200 μg and an XK-16 column, equilibrated with        1×PBS, pH 7.4 (1.0 ml/min); collect fractions by UV absorption        at 280 nm.    -   Dialysis of the antibody solution at 4° C. overnight in 1×3.0 l        PBS, pH 7.4 and Slide-A-Lyzer Dialysis Cassettes 20,000 MWCO.        Determination of protein concentration using naked antibody vs.        ADC adjusted to identical protein concentrations.        Adjust protein concentration to 5.0 mg/ml (=3.42×10⁻⁵M) and        bring to sterile conditions by filtration. Store at 4° C.

1. A conjugate comprising (a) an amatoxin comprising (i) an amino acid 4with a 6′-deoxy position; and (ii) an amino acid 8 with an S-deoxyposition; (b) a target-binding moiety; and (c) a cleavable linkerlinking said amatoxin and said target-binding moiety.
 2. The conjugateof claim 1 having structure I

wherein: R² is S; R³ is selected from —NHR⁵, —NH—OR⁵, and —OR⁵; R⁴ is H;and wherein one of R⁵ is -L_(n)-X, wherein L is a cleavable linker, n isselected from 0 and 1, and X is a target-binding moiety, and wherein theremaining R⁵ are H.
 3. A conjugate comprising (a) an amatoxin comprising(i) an amino acid 4 with a 6′-deoxy position; and (ii) an amino acid 8with an S-deoxy position; (b) a target-binding moiety; and (c)optionally a linker linking said amatoxin and said target-bindingmoiety.
 4. The conjugate of claim 3 having structure I

wherein: R² is S; R³ is selected from —NHR⁵, —NH—OR⁵, and —OR⁵; R⁴ is H;and wherein one of R⁵ is -L_(n)-X, wherein L is a linker, n is selectedfrom 0 and 1, and X is a target-binding moiety, and wherein theremaining R⁵ are H.
 5. A pharmaceutical composition comprising theconjugate of claim
 1. 6. (canceled)
 7. A construct comprising (a) anamatoxin comprising (i) an amino acid 4 with a 6′-deoxy position; and(ii) an amino acid 8 with an S-deoxy position; and (c) a cleavablelinker moiety carrying a reactive group Y for linking said amatoxin to atarget-binding moiety.
 8. A method for treating cancer, comprisingadministering the conjugate according to claim 1 to a patient havingcancer.
 9. The method of claim 8, wherein the cancer is selected frombreast cancer, pancreatic cancer, cholangiocarcinoma, colorectal cancer,lung cancer, prostate cancer, ovarian cancer, prostate cancer, stomachcancer, kidney cancer, malignant melanoma, leukemia, and/or malignantlymphoma.